1. Field of the Invention
The present invention relates generally to an optical device capable of operating at high speeds, and more particularly to an optical device having a package structure fit for characteristic impedance matching and grounding enhancement in an optical receiver.
2. Description of the Related Art
In a trunk optical communication system, a 10 Gb/s system has been put to practical use and its introduction has been started at present. As seen in explosive spread of Internet or the like, it is considered that the demand for the 10 Gb/s system will be rapidly increased in the future, and in an optical transmitter and an optical receiver for the 10 Gb/s system it is strongly desired to attain further cost reduction, mass production, and size reduction.
On the other hand, also in an optical wavelength division multiplexing system as a next-term system, the 10 Gb/s system is considered to become a base system. Therefore, the cost reduction, mass production, and size reduction of an optical transmitter and an optical receiver for the 10 Gb/s system will become an important issue also in constructing the next-term system. This issue cannot be attained by a conventional package structure, and it is therefore desired to provide an optical device having a novel package structure.
Referring to FIGS. 1A and 1B, there are shown a perspective view and a sectional view of a conventional O/E module (optical receiver), respectively. As shown in FIG. 1A, this O/E module includes a package 4 into which an optical fiber 2 is introduced, and a ceramic terminal 6 for outputting a high-speed electrical signal obtained by converting an optical signal transmitted by the optical fiber 2. A plurality of leads 8 for d.c. power or low-speed signal are provided on the opposite side surfaces of the package 4. This conventional structure is called also as a butterfly package from its appearance. As shown in FIG. 1B, a carrier 10 is fixed inside the package 4, and a photodetector 12 and an IC chip 14 for preamplification are provided on one side surface and the upper surface of the carrier 10, respectively. The ceramic terminal 6 is composed of a conductor layer 16 and a ceramic block 18 holding the conductor 16.
An optical signal output from the optical fiber 2 is converged by a lens 20 and next converted into an electrical signal by the photodetector 12. The electrical signal output from the photodetector 12 is amplified by the IC chip 14 and next output from this O/E module through the ceramic terminal 6.
In the above-mentioned prior art, the use of the ceramic terminal 6 excellent in high-speed operability can provide an optical device capable of operating at high speeds. However, since the package 4 and the carrier 10 are separate members, and the ceramic terminal 6 used is expensive, it is difficult to reduce cost.
In a relatively low-speed optical receiver in the prior art, a so-called coaxial package structure capable of attaining cost reduction is adopted in some case. However, such a conventional low-cost package structure has a problem such that it is difficult to ensure high-speed operability.